This invention relates to electro-hydraulic braking systems of the kind in which at least one electrically operated actuator is provided in a brake line between a fluid source and a brake, operation of the electrically operated actuator selectively connecting and disconnecting the brake to the pressure source, and in which a pressure sensor is provided which is adapted to sense the fluid pressure in a part of the braking system.
The provision of at least one pressure sensor in the hydraulic circuit enables a measure of circuit performance and behaviour to be made. Because the system comprises both electrical circuitryxe2x80x94for control of the actuators and interrogation of the pressure sensorsxe2x80x94and hydraulic circuitry, there is a problem of leakage of fluid from the hydraulic circuit affecting the electrical circuit.
In the past, it has been known to incorporate the hydraulic and electrical components into a two part housing. One part of the housing contains the electrical circuitry for controlling the actuators. The other part contains the hydraulic passages for the brake fluid. Where the electrically operated actuators are controlled by a solenoid which comprises of an armature working with a coil, the coils of the solenoid are adapted to be fixed relative to and extend from the first housing. The armature is then adapted to extend from the second housing and be sealed therewith. As the two halves of the housing are placed together, the coils pass over the armature to complete the magnetic circuit of the electrically-controlled actuators.
The applicant is aware of U.S. Pat. No. 6,007,162 which discloses a braking system in which a number of pressure sensors are housed within respective casings that are pressed into engagement with a respective pressure conduit extending from the actuators in order to permit an increase of the pressure to be obtained. However, each sensor is housed separately and they cannot be readily removed for servicing.
In accordance with the present invention we provide an electro-hydraulic braking system in which at least one electrically operated actuator is provided in a brake line between a pressure source of hydraulic fluid and a brake, operation of the electrically operated actuator selectively connecting and disconnecting the brake to the pressure source, and in which at least one pressure sensor is adapted to sense fluid pressure in a part of the braking system, the system being characterised by a housing having at least three discrete housing portions, a first portion being adapted to contain electrical drive circuitry for the actuator, a second portion being adapted to contain hydraulic fluid passages to and from the electrically operated actuator, and a third portion being adapted to house a plurality of pressure sensors, in which on assembly of the housing electrical contacts from the pressure sensors in the third portion provide a connection between the pressure sensors and the electrical drive circuitry contained in the first portion, and a respective hydraulic fluid passage extending from each of the pressure sensors in the third portion provides a connection between the pressure sensors and corresponding hydraulic fluid passages in the second portion.
Thus, the invention provides a separate housing portion a plurality of pressure sensors. This allows the pressure sensor(s) to be easily replaced or removed as a group from both the electrical circuitry and the hydraulic circuits.
Preferably, the third portion comprises a body having a plurality of through bores, a pressure sensor being provided within a respective bore. Each sensor may be provided within a tube which is adapted to fit within a bore in the body, an end portion of the tube extending outwardly away from the bore. The end portion of tube can be inserted into a corresponding recessed hole in the second portion to provide a hydraulic connection. Electrical connections to the pressure sensor may extend from one end of the tube.
As an alternative the body may be split into two halves which clamp around the tubes containing the pressure sensors. Of course, the tubes could be omitted in at least one alternative.
A temperature sensor may be provided within the pressure sensor housing to allow the temperature of the hydraulic fluid to be measured.
A temperature sensor may be provided for each pressure sensor, to measure the temperature of the fluid reaching each pressure sensor. Alternatively, any number of temperature sensors may be provided.
The third portion housing the pressure sensors may further include an engagement means adapted to enable the pressure sensor housing to be mechanically secured to the first housing portion. The engagement means may comprise a number of holes 30, illustrated in FIGS. 1, 3(a), and 3(b), adapted to receive one or more bolts which engage with threaded blind bores 32, illustrated in FIG. 2, in the first housing portion. Alternatively, the pressure sensor housing may be a snap-fit engagement with the first housing portion.
The openings in the ends of the tubes which allow fluid from the second housing to reach the pressure sensors may extend axially in the same direction as the axis of the coils for the solenoid valves, so that the pressure sensor tubes readily slide into the respective holes in the second portion simultaneous with the coils sliding around and onto the armatures of the flow valves during assembly.
An annular seal such as an elastomeric seal may be provided around the end of each protruding portion of tube to form a fluid tight seal within the respective hole in the second portion on assembly. The seal may be located in a groove extending around the tube. A second annular seal may be provided between the tube and the bore in the third portion.
Alternatively, or additionally, an elastomeric seal may be provided in a recess which links the ends of all the tubes. The seal may be located in a recess in a face of the third body. The individual seals could then be omitted from each tube. In yet another alternative, the recess linking the ends of the tubes may be adapted to connect a portion of the end of the tube to atmosphere when the third portion is pressed against the second portion to ensure there is no difference between the pressure on the side of the second housing and the measured pressure on the side of the third housing.
The electrical circuitry may be sealed within the first portion at least with respect to the interface between the first portion and the second portion.
One or more solenoid coils may be located in or mounted on the first portion, each coil forming a part of a solenoid for a respective electrically controlled valve. The armature corresponding to each valve may be supported by the second portion. The armature may be sealed to prevent leakage of fluid past the armature/housing interface. The armature may pass into the coil when the first and second housing portions are assembled together.
The third portion may be adapted to be received, at least partially, within a recess in the first portion. When the first and second portions are assembled, the third portion may be completely encased by the first and second portions.
The first and second housing portions may be provided with a continuous seal around a perimeter of the mating faces to seal the inside of the two housing portions together when assembled.